Method and cable for connecting electronic equipment to another electronic equipment

ABSTRACT

A connection method and a connecting cable for improving transmission of low-frequency signals and reducing the radiation level of high-frequency signals. To connect electronic devices via a connecting cable, the region between the ends of the signal line of a connecting cable is shielded by a first external conductor. Then one end of the first external conductor is connected to a reference potential of a first electronic device. The first external conductor is shielded by a second external conductor, and the second external conductor is connected to a reference potential of a second electronic device. The reference potentials of the first and reference potentials of the second electronic devices are coupled through a stray capacity between the first external conductor and the second external conductor. The length of opposition between the first and second external conductors is adjusted according to a frequency for suppressing radiation.

FIELD OF THE INVENTION

The present invention relates to a method for connecting electronicdevices and a connecting cable.

BACKGROUND OF THE INVENTION

As shown in FIGS. 12(a) and (b), to transmit a signal from a firstelectronic device la to a second electronic device 1 b, a connection isprovided as shown in FIG. 12(a) or FIG. 12(b), using a connecting cable4 in which a signal line 2 is shielded by a first external conductor 3a.

In the connection of FIG. 12(a), one end of the signal line 2 isconnected to the signal output 5 of the first electronic device 1 a, theother end of the signal line 2 is connected to the signal input 6 of thesecond electronic device 1 b, one end of the first external conductor 3a is connected to a frame 7, which is the reference potential of thefirst electronic device 1 a, and the other end of the first externalconductor 3 a is connected to a frame 8, which is the referencepotential of the second electronic device 1 b.

In such connection, if there is no potential difference between theframes 7 and 8, good signal transmission can be realized, but, if thesignal level is low and there is a potential difference between theframes 7 and 8, then noise mixes into the signal input 6 of the secondelectronic device 1 b.

In this case, one-point grounding connects the first external conductor3 a only to the frame 7 of the first electronic device 1 a, withoutconnecting the other end of the first external conductor 3 a to theframe 8 of the second electronic device 1 b.

However, assuming the case in which the first electronic device 1 a andthe second electronic device 1 b are spaced a long distance apart fromeach other and low-frequency signals (the frequency band is several tensKHz to several tens MHZ) and high frequency signals (the frequency bandis several tens MHZ or higher) are transmitted by the signal line 2, orthe case in which a digital signal of a high-frequency is transmitted,the one-point grounding as shown in FIG. 12(b) problematically increasesthe level of undesired radiation of high-frequency signals from thefirst external conductor 3 a into the air.

In this conventional example, the description has been made to oneconnecting cable 4 by way of example, but, in the connection by aplurality of connecting cables which are placed in parallel between thefirst electronic device 1 a and the second electronic device 1 b, thereis a problem that noise radiated from the respective juxtaposedconnecting cables 4 interferes with each other to further increase theundesired radiation level.

It is the object of the present invention to provide a connection methodand a connecting cable, which enable good transmission of low-frequencysignals as well as lowering the radiation level of high-frequencysignals in such case as described above.

BRIEF SUMMARY OF THE INVENTION

The method for connecting electronic devices of the present invention ischaracterized by connecting a first electronic device 1 a and a secondelectronic device 1 b with a first external conductor being one-pointgrounded, and connecting an end of a second external conductor on thesecond electronic device 1 b side to reference potential of the secondelectronic device 1 b for high-frequency signals, thereby providing aconnection between the electronic devices, and enabling goodtransmission of low-frequency signals as well as lowering the radiationlevel of high-frequency signals.

The method for connecting electronic devices as set forth in a firstembodiment is characterized in that, to connect electronic devices by aconnecting cable, the part between the ends of the signal line of theconnecting cable is shielded by a first external conductor, one end ofthe first external conductor is connected to the reference potential ofone electronic device of the electronic devices, the first externalconductor is shielded by a second external conductor, the secondexternal conductor is connected to the reference potential of the otherelectronic device, whereby the reference potential of one electronicdevice and the reference potential of the other electronic device arecoupled through the stray capacity between the first external conductorand the second external conductor.

With this arrangement, the first external conductor is one-pointgrounded to the first electronic device preventing the difference in thereference potential levels of the first and second electronic devicesfrom being brought into the second electronic device, whereby goodtransmission of low-frequency signals can be accomplished, and theimpedance of the first external conductor to high-frequency signalsdecreases, reducing undesired radiation.

The method for connecting electronic device as set forth in a secondembodiment is characterized in that, to connect electronic devices by aconnecting cable, the signal lines of a plurality of connecting cablesare respectively shielded by a first external conductor between the endsthereof, one of the respective first external conductors is connected tothe reference potential of one electronic device of the electronicdevices, the respective first external conductors are shielded by acommon second external conductor, and the second external conductor isconnected to the reference potential of the other electronic device,whereby the reference potential of one electronic device and thereference potential of the other electronic device are coupled throughthe stray capacity between the first and second external conductors.

With this arrangement, the respective first external conductors areone-point grounded to the first electronic device preventing thedifference in the reference potential level between the first device andsecond electronic devices from being brought into the second electronicdevice, whereby good transmission of low-frequency signals can beaccomplished, and the impedance of the respective first externalconductors decreases, reducing undesired radiation.

The method for connecting electronic devices as set forth in a thirdembodiment is characterized in that, to connect electronic devices by aconnecting cable, the signal lines of a plurality of connecting cablesare respectively shielded by a first external conductor in the partbetween the ends thereof, one end of the respective first externalconductor is connected to the reference potential of one electronicdevice of the electronic devices, the respective first externalconductors are electrically connected to each other in the other endthereof, the respective first external conductors are shielded by acommon second external conductor, and the second external conductor isconnected to the reference potential of the other electronic device,whereby the reference potential of one electronic device and thereference potential of the other electronic device are coupled throughthe stray capacity between the first external conductor and the secondexternal conductor.

With this arrangement, because the first external conductors areelectrically connected to each other, in addition to the construction ofthe second embodiment, the system of each first external conductor forhigh-frequency signals is stable as compared with the case in which thefirst external conductors are not positively made equipotential in theother end thereof, and no independent standing wave occurs in therespective first external conductors.

The method for connecting electronic devices as set forth in a fourthembodiment is characterized in that the length of opposition between thefirst and second external conductors is adjusted according to afrequency for which undesired radiation is to be suppressed.

The method for connecting electronic devices as set forth in a fifthembodiment is characterized in that the adjustment is performed byconnecting, between the first and second external conductors, a elementhaving a capacitance according to the frequency for which undesiredradiation is to be suppressed.

With this arrangement, the undesired radiation of the high frequencyband can be reduced by the action of a stray capacity between the firstand second external conductors, and the cutoff frequency of the lowfrequency band for high frequencies is adjusted by the capacitor elementconnected between the first and second external conductors to suppressundesired radiation.

The method for connecting electronic devices as set forth in a sixthembodiment is characterized in that, to connect electronic devices by aconnecting cable, signal lines of a plurality of connecting cables arerespectively shielded by first external conductors between the endsthereof, one end of the respective first external conductors isconnected to the reference potential of one of the electronic devices,the other ends of the respective first external conductors areelectrically connected to each other, the respective first externalconductors are shielded by a common second external conductor, thesecond external conductor is connected to reference potential of theother electronic device, and the other ends of the respective firstexternal conductors are electrically connected to each other, andcovered with a third external conductor which contacts the outside of abundle of the first external conductors of a plurality of connectingcables and opposed-to the second external conductor, whereby thereference potential of one electronic device and the reference potentialof the other electronic device are coupled through a stray capacitybetween the second external conductor and the third external conductor.

With this arrangement, the bundle of the first external conductors of aplurality of connecting cables is covered with a third externalconductor, thereby connecting the first external conductor to thereference potential of the second electronic device by the straycapacity generated between the second and third external conductors, andthus the stray capacity generated between the second and third externalconductors does not depend on the diameter of the respective firstexternal conductors.

The method for connecting electronic devices as set forth in a seventhembodiment is characterized in that the length of opposition between thesecond and third external conductors is adjusted according to thefrequency with which undesired radiation is to be suppressed.

The method for connecting electronic devices as set forth in an eighthembodiment is characterized in that the adjustment is performed byconnecting, between the third and second external conductors, acapacitor element having a capacitance corresponding to the frequencywith which undesired radiation is to be suppressed. With thisarrangement, the undesired radiation of the target frequency can beselectively suppressed.

The method for connecting electronic devices as set forth in a ninthembodiment is characterized in that at least one of the second and thirdexternal conductors is a braided wire.

The method for connecting electronic devices as set forth in a tenthembodiment is characterized in that a sheet made up of a first andsecond conductor sheets opposed to each other through an insulation filmis wound around the connecting cable, making the inner first conductorsheet as the third external conductor and the outer second conductorsheet as the second external conductor, whereby the reference potentialof one electronic device and the reference potential of the otherelectronic device are coupled through the stray capacity between thefirst conductor sheet and the second conductor sheet.

With this arrangement, the number of steps in the terminal process canbe reduced and large stray capacity can be obtained by thinning thethickness of the insulation film of the sheet.

The method for connecting electronic devices as set forth in an eleventhembodiment is characterized in that, to connect electronic devices by aconnecting cable, signal lines of a plurality of connecting cables arerespectively shielded by a first external conductor between one end andthe other end thereof, one end of the respective first externalconductors is connected to reference potential of one electronic deviceof the electronic devices, and the other ends of the respective firstexternal conductors are electrically connected to each other andconnected to reference potential of the other electronic device, therebypreventing a standing wave from being independently generated in thefirst external conductor of each connecting cable.

With this arrangement, as compared with the case in which the firstexternal conductors are not positively made equipotential to each otherat the other end thereof, the system of each external conductor towardhigh-frequency signals becomes stable, and a standing wave does notseparately occurs in the respective first external conductors, so it issuitable for transmission of digital signals.

The connecting cable as set forth in a twelfth embodiment ischaracterized by comprising a first external conductor for shieldingsignal lines between one end and the other end thereof, and a secondexternal conductor opposed to the first external conductor through aninsulator and for shielding the first external conductor, wherein thefirst external conductor on one end of the signal line is connected toreference potential of one electronic device connected by the signalline, and the second external conductor on the other end of the signalline is connected to reference potential of the other electronic device.

The connecting cable as set forth in a thirteenth embodiment ischaracterized by comprising a first external conductor for shielding thepart between the ends of a signal line, and a second external conductoropposed to the first external conductor through an insulator and forshielding part of the other end of the first external conductor, whereinthe first external conductor on one end of the signal line is connectedto reference potential of one electronic device connected by the signalline, the second external conductor on the other end of the signal lineis connected to reference potential of the other electronic device, andat least one parameter of the length of opposition between the first andsecond external conductors, the electrode distance between the first andsecond external conductors, and the material of the insulator are setaccording to a frequency with which undesired radiation is to besuppressed.

The connecting cable as set forth in a fourteenth embodiment ischaracterized in that there is provided a capacitor element connectedbetween the first and second external conductors, and the capacitance ofthe capacitor element is set to a capacitance corresponding to thefrequency with which undesired radiation is to be suppressed.

The connecting cable as set forth in a fifteenth embodiment ischaracterized in that the second external conductor is a braided wire,and the distal end of the second external conductor of a braided wire isfolded back to the side of one end of the signal line.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of a connection method and connectingcable according to embodiment 1 of the present invention;

FIG. 2 is an explanatory view of a stray capacity formed between thefirst and second external conductors according to the embodiment 1;

FIG. 3 is a cross-sectional view of a connecting cable for a connectionmethod according to embodiment 2;

FIG. 4 is a cross-sectional view of a connecting cable showing anotherembodiment of the embodiment 2;

FIG. 5 is a cross-sectional view of a connecting cable for a connectionmethod according to embodiment 3;

FIG. 6 is a cross-sectional view of a connecting cable showing anotherembodiment of the embodiment 3;

FIGS. 7(a) to (e) are flow diagrams of a terminal process of aconnecting cable used in a connection method according to embodiment 4of the present invention;

FIG. 8 is a perspective view showing the completion of the terminalprocess of the embodiment 4;

FIGS. 9(a) to (e) are flow diagrams of a terminal process of aconnecting cable used in a connection method according to embodiment 5of the present invention;

FIGS. 10(a) to (d) are flow diagrams of a terminal process of aconnecting cable used in a connection method according to embodiment 6of the present invention;

FIG. 11 is an explanatory view of a connecting cable used in aconnection method according to embodiment 7 of the present invention;and

FIGS. 12(a) and (b) are partially cutaway views of a connecting cablefor explaining a conventional connection method.

DETAILED DESCRIPTION OF THE INVENTION

Now, the respective embodiments of the present invention are describedaccording to FIGS. 1 to 11.

Embodiment 1

FIG. 1 and FIG. 2 show the first embodiment.

A connecting cable 4 for connecting a first electronic device 1 a and asecond electronic device 1 b is surrounded by the first externalconductor 3 a of a braided wire so as to be shielded in most of the fulllength thereof, over one end 4 a to the other end 4 b of a signal line 2connecting between the signal output 5 of the first electronic device 1a and the signal input 6 of the second electronic device 1 b.

The outside of the first external conductor 3 a is covered with a firstexternal sheath 9 a, and the further outside of it is surrounded by thesecond external conductor 3 b of a braided wire over one end to theother end thereof for shielding. The outside of the second externalconductor 3 b is covered with a second external sheath 9 b.

One end of the first external conductor 3 a is connected to a frame 7 ofthe reference potential of the first electronic device 1 a. The end ofthe first external conductor 3 a is not connected to a frame 8 of thereference potential of the second electronic device 1 b.

The end portion on the other end 4 b side of the second externalconductor 3 b is connected to the frame 8 of the reference potential ofthe second electronic device 1 b through a lead 11.

With this arrangement, since the connecting cable 4, when looking thesecond electronic device 1 b from the first electronic device 1 a, isone-point grounded to the frame 7 of the first electronic device 1 a forlow-frequency signal band (frequency band of several tens KHz to severaltens MHZ), a signal can be successfully transmitted to the signal input6 of the second electronic device 1 b even if a potential difference isgenerated between the frame 7 of the first electronic device 1 a and theframe 8 of the second electronic device 1 b. For a high-frequency signalband (frequency band of several tens MHZ or higher), the frame 7 of thefirst electronic device 1 a and the frame 8 of the second electronicdevice 1 b are coupled through a stray capacity C generated between thefirst and second external conductors 3 aand 3 b, which are opposed toeach other through the first external sheath 9 a, as shown in FIG. 2,the impedance of the first external conductor 3 a in the high frequencysignal band can be made low even though the first external conductor 3 ais one-point earthed.

Accordingly, the level of the signal induced in the first externalconductor 3 a according to the signal applied to the signal line 2 andundesirably radiated to the outside can be significantly reduced ascompared with the prior art.

Although the first and second external conductors 3 a and 3 b are bothof a braided wire, a similar effect can be expected even if both or oneof them is replaced by aluminum foil or metal pipe.

Embodiment 2

FIG. 3 and FIG. 4 show a second embodiment.

The second external conductor 3 b of the first embodiment is providedopposite to the most part of the first external conductor 3 a, but, inembodiment two, it is partially provided on the other end 4 b side ofthe first external conductor 3 a so as to be opposed to the firstexternal conductor 3 a over only an opposed length D. The opposed lengthD is set to an opposed distance needed to generate a stray capacity,which can make the impedance of the first external conductor 3 a highfor a low-frequency signal region, and can make the impedance of thefirst external conductor 3 a low in a high-frequency signal region.

With this arrangement, by changing the opposed length D, the frequencyfor which undesired radiation is to be suppressed can be freelyadjusted. Further, since the length of the second external conductor 3 bcan be made short as compared with the embodiment 1, the connectingcable 4 can easily be manufactured.

Further, as shown in FIG. 4, by interposing a ceramic capacitor 12 ofseveral tens pF to tens of thousands pF between the first externalconductor 3 a and the second external conductor 3 b on the secondelectronic device 1 b side of the connecting cable 4 shown in FIG. 3,the undesired radiation of part of the high frequency region of alow-frequency signal region can also be reduced. Specifically, by addinga large capacitance which cannot be obtained by the above stray capacityby means of the ceramic capacitor 12, the impedance of the connectingcable in the low-frequency signal region can be reduced in thelow-frequency signal region of several tens KHz to 10 MHZ.

In addition, a similar effect can be expected even if the first andsecond external conductors 3 a and 3 b are both made up of a braidedwire, or both or one of them is replaced by aluminum foil or metal pipe.

Embodiment 3

FIG. 5 and FIG. 6 show the third embodiment.

In the first and second embodiments, the signal line 2 covered with thefirst external sheath 9 a is provided within the single second externalconductor 3 b. However, in the third embodiment, a plurality of signallines 2 each covered with the first external sheath 9 a is providedwithin a single second external conductor 3 b.

In FIG. 5, the respective first external conductors 3 a are tiedtogether in the other end thereof by a tying band 13 of an insulator (ora conductor), and by tightening the tying band 13, the respective firstexternal conductors 3 a are brought in contact with each other to makeelectrical connection. The remaining points are the same as FIG. 3.

Further, by winding a single wire or braided wire around the firstexternal conductor 3 a so as to tie them together in the other endthereof, and soldering them rather than tying the first externalconductor 3 a together in the other end thereof, a similar effect canalso be obtained. If the first external conductor 3 a and the secondexternal conductor 3 b are tied together by a conductor in the other endthereof, the first external conductor 3 a and the second externalconductor 3 b are insulated from each other so that they do not conductthrough a lead 11.

With this arrangement, even if signals of different frequencies areapplied to the plurality of signal lines 2, no standing wave occurs ineach of the first external conductor 3 a of different frequencies, andthus the system of the plurality of first external conductors 3 a in ahigh-frequency signal region becomes stable.

In FIG. 6, a ceramic capacitor 12 of a small capacitance is added to theconstruction shown in FIG. 5, and the remaining points are the same asFIG. 4.

In addition, even if the first and second external conductors 3 a and 3b are comprised of a braided wire, or both or one of them is replaced byaluminum foil or metal pipe, a similar effect can be expected.

Embodiment 4

FIGS. 7(a) to (e) and FIG. 8 show the fourth embodiment.

In the embodiment 3, the tying process of the plurality of firstexternal conductors 3 a and the soldering process between the ceramiccapacitor 12 are independently carried out, but, in the fourthembodiment, as shown in FIG. 7(a), one lead 12 a of the ceramiccapacitor 12 is made to run along the first external conductors 3 a, andthe outside of them is covered with a heat-resistant, heat-shrinkabletube 14.

On both ends of the inside of the heat-resistant, heat-shrinkable tube14, an adhesive tape 15 is provided, and in the center, a C-like ring16, which can deform so that the diameter of it can be decreased, isset. To the ring 16, solder or solder paste is previously applied.

The heat-resistant, heat-shrinkable tube 14, in which the adhesive tape15 and the ring 16 are set, fits over the first external conductors 3 aso that one lead 12 a of the ceramic capacitor 12 lies between the firstexternal conductors 3 a and the ring 16, and then the outside of theheat-resistant, heat-shrinkable tube 14 is heated with a hot-air heater(not shown) such as a hot blaster.

By heating, the heat-resistant, heat-shrinkable tube 14 shrinks so thatthe diameter of it decreases, as shown in FIG. 7(c). The ring 16 flittedin the heat-resistant, heat-shrinkable tube 14 also deforms so that thediameter of it decreases to tighten and tie together the plurality offirst external conductors 3 a. Further, when the temperature of the ring16 is elevated by the heat from the above hot-air heater, the solder orsolder paste on the ring 16 dissolves, and the ring 16 and the lead 12 aof the ceramic capacitor 12 and the plurality of first externalconductors 3 a are soldered. Consideration is given so that the shrunkheat-resistant, heat-shrinkable tube 14 is stuck on the tied firstexternal conductors 3 a by the adhesive tape 15 and it is not displaced.

Then, as shown in FIG. 7(d), the other lead 12 b of the ceramiccapacitor 12 is soldered to the second external conductor 3 b, andfinally, as shown in FIG. 7(e), it is covered with a heat-shrinkabletube 18, heated, and finished as shown in FIG. 8.

In this embodiment, as shown in FIG. 7(a), the end portion of the secondexternal conductor 3 b is folded to the first electronic device 1 aside, and terminated through the bundling by a tying band 17, as shownin FIG. 8, thereby to give consideration that, if the second externalconductor 3 b is a braided wire, an assembly failure, such as part ofthe broken braid being put in contact with the first external conductors3 a, is difficult to occur.

In addition, even if the first external conductors 3 a are comprised ofa braided, or replaced by aluminum foil or metal pipe, a similar effectcan be expected.

Embodiment 5

FIGS. 9(a) to (e) show the fifth embodiment.

In the fourth embodiment, by opposing the second external conductor 3 bto the plurality of external —conductors 3 a, —the stray capacity C isproduced, but the capacitance of it varies depending on the thicknessand material of the first external sheath 9 a surrounding the outside ofthe first external conductors 3 a. In the fifth embodiment, by providinga third external conductor 3 c between the first and second externalconductors 3 a and 3 b, the stray capacity is stabilized.

First, a plurality of cables shielded by the first external conductor 3a is tied together by a tying band 13 as shown in FIG. 9(a), as in FIG.5. Then, the outside of the first external conductors 3 a is coveredwith a third cylindrically shaped external conductor 3 c, as shown inFIG. 9(b), thereby to contact the first external conductors 3 a with thethird external conductor 3 c for electrical connection. Then, as shownin FIG. 9 (c), the third external conductor 3 c is covered with the athird external sheath 9 c, and as shown in FIG. 9(d), a second externalconductor 3 b is provided, and as shown in FIG. 9(e), the secondexternal conductor 3 b is connected to the frame 8 of the secondelectronic device 1 b through a lead 11, as in the above describedembodiment. In addition, the second external conductor 3 b may becovered with a second external sheath (not shown).

Such covered third external conductor 3 c and the first externalconductors 3 a are strongly tied together by a tying band 20 a in theportion where they are abutting each other, for ensuring the electricconnection of the third external conductor 3 c with the first externalconductors 3 a. Similarly, the outside of the second external conductor3 b is bundled by the tying band 20 b to secure the opposing faces ofthe third external conductor 3 c and the second external conductor 3 b.

With this arrangement, the end portions of the first external conductors3 a are connected to the frame 8 of the second electronic device 1 bthrough the stray capacity formed between the second external conductor3 b and the third external conductor 3 c. Further, the magnitude of thestray capacity depends on the parameters such as the opposed length anddistance between the second external conductor 3 b and the thirdexternal conductor 3 c, and a predefined capacitance can be obtainedeven if the distance between the first external conductors 3 a and thesecond external conductor 3 b is changed.

Also in the fifth embodiment, the end portion of the second externalconductor 3 b may be terminated by folding it to the first electronicdevice 1 a side, as in the fourth embodiment, or to increase the straycapacity, a ceramic capacitor may be connected between the secondexternal conductor 3 b and the first external conductors 3 a, or betweenthe second external conductor 3 b and the third external conductor 3 c.

Further, although the first, second, and third external conductors 3 a,3 b, and 3 c are all comprised of a braided wire, a similar effect canbe expected even if one, two, or three of them are replaced by aluminumfoil or metal pipe.

Embodiment 6

FIGS. 10(a) to (d) show the sixth embodiment. In the fifth embodiment,the first external conductors 3 aare covered with the third externalconductor 3 c, and thereafter the third external sheath 9 c, secondexternal conductor 3 b, and second external sheath (not shown) aresequentially formed to make up the connecting cable 4, but, in the sixthembodiment, the number of steps in the termination process can bereduced more than the fifth embodiment.

First, a plurality of cables shielded by the first external conductors 3a are tied together by a tying band 13 in a manner similar to FIG. 5, asshown in FIG. 10(a). Then, a previously made laminated film 21 is woundaround it, as shown in FIG. 10 (b) and FIG. 10(c), and it is only neededto tie up with a tying band 22 from the outside of the laminated film 21wound around as shown in FIG. 10(d), the termination process iscompleted.

Specifically, the laminated film 21 is formed by a first conductor sheet30 c and a second conductor sheet 30 b, which are opposed to each otherwith an insulation film 23 being sandwiched therebetween.

With this arrangement, by winding around the laminated film 21, thefirst external conductors 3 a and the first conductor sheet 30 c arebrought in contact with each other for electrical connection, and thedesired stray capacity is formed between the first conductor sheet 30 cand the second conductor sheet 30 b, as in the fifth embodiment.Further, a large stray capacity can be obtained by increasing thethickness of the insulation film 23.

In addition, if the laminated film 21 is simply wound around, the firstconductor sheet 30 c on the inner surface side is put on the secondconductor sheet 30 b on the outer surface side at the winding end toproduce electrical continuity between the two, and thus, specifically,at least at the winding end of the laminated film 21, the firstconductor sheet 30 c and the second conductor sheet 30 b are isolated byinterposing an insulation film between the two.

Further, although in the above description, the first externalconductors 3 a and the first conductor sheet 30 c are caused to abutwith each other and electrically connected by winding the laminated film21, a construction may be provided in which, after the laminated film 21is wound around the first external sheath 9 a, the lead extracted fromthe first conductor sheet 30 c is connected to the first externalconductors 3 a.

Moreover, in this embodiment, the laminated film 21 has been describedas a three-layer structure in which the first conductor sheet 30 c andthe second conductor sheet 30 b are opposed to each other through theinsulation film 23. However, to prevent electrical continuity from beingproduced between the first conductor sheet 30 c and the second conductorsheet 30 b at the winding end when the laminated film 21 is simply woundaround, it is possible to use a four-layer or five-layer laminated filmin which at least one of the surface of the first conductor sheet 30 cand the surface of the second conductor sheet 30 b is covered with aninsulation film, and extract leads from the first conductor sheet 30 cand the second conductor sheet 30 b. With this arrangement, the mountingefficiency further increases.

Embodiment 7

FIG. 11 shows the seventh embodiment.

Each embodiment above describes the case in which low-frequency signalsand high-frequency signals are transmitted from the first electronicdevice 1 a to the second electronic device 1 b. However, the seventhembodiment shows a specific example of the method for connectingelectronic devices for digital use only, in which high-frequency digitalsignals are transmitted by a plurality of juxtaposed connecting cables 4a, 4 b, . . . 4 n.

The end portions of the respective first external conductors 3 a of theconnecting cables 4 a, 4 b, . . . 4 n on the first electronic device 1 aside are respectively connected to the frame (corresponding to 7 ofFIG. 1) of the first electronic device (corresponding to 1 a of FIG. 1)through a lead. A first external sheath 9 a covers the outside of thefirst external conductors 3 a.

The end portions of the first external conductors 3 a of the connectingcables 4 a, 4 b, . . . 4 n on the second electronic device 1 b side arebundled together by a tying band 23 of conductor or insulator toelectrically connect the first external conductors 3 a in the other endthereof, and they are connected to the reference potential of the secondelectronic device 1 b through a lead 11.

With such arrangement, no separate standing wave occurs in the firstexternal conductor of each connecting cable, so a stable operation andthe reduction of undesired radiation can be expected.

Further, a similar effect can also be expected by soldering the firstexternal conductors 3 a to each other in the other end thereof by a ringor a braided wire instead of the tying band 23, and connecting them tothe reference potential of the second electronic device 1 b through thelead 11.

Although, in each embodiment described above, the signal line of oneconnecting cable of the plural number (two), the signal line of oneconnecting cable may be single, as seen in a coaxial cable.

What is claimed is:
 1. A method for connecting electronic devicescomprising: providing a plurality of cables each having at least twoends; shielding signal lines of the plurality of connecting cablesbetween the ends thereof by first external conductors, respectively;connecting one end of the first external conductors to a referencepotential of at least one first electronic device, and electricallyconnecting the other ends of the first external conductors to eachother; shielding said first external conductors by a common secondexternal conductor; connecting the second external conductor to areference potential of a second electronic device, electricallyconnecting the other ends of the first external conductors to eachother, and covering said first external conductors by a third externalconductor which contacts the outside of a bundle of the first externalconductors of the plurality of connecting cables so as to oppose thesecond external conductor; and coupling the reference potential of thefirst and second electronic devices through a stray capacity between thesecond and third external conductors.
 2. A method for connectingelectronic devices as set forth in claim 1, wherein the length ofopposition between the second and third external conductors is adjustedaccording to a frequency for suppressing radiation.
 3. A method forconnecting electronic devices as set forth in claim 1, wherein theadjustment is performed by connecting, between the second and thirdexternal conductors, a capacitor element having a capacitancecorresponding to the frequency for suppressing radiation.
 4. A methodfor connecting electronic devices as set forth in claim 1, wherein atleast one of the second and third external conductors is a braided wire.5. A method for connecting electronic devices as set forth in claim 1,wherein a sheet comprising inner first and outer second conductor sheetsopposing each other through an insulation film winds around theconnecting cable, wherein the inner first conductor sheet forms thethird external conductor and the outer second conductor sheet forms thesecond external conductor, whereby the reference potential of the firstand second electronic devices are coupled through the stray capacitybetween the inner first and outer second conductor sheets.